Conformal retro-modulator optical devices

ABSTRACT

A conformal retro-modulator optical apparatus. The apparatus includes an array of multiple quantum well devices disposed in a thin array. A plastic support element is bonded to the thin array, the plastic support element having a thickness greater that of the thin array. The plastic support element is preferably plastic at elevated temperatures above room temperature, thereby allowing the plastic support element and the thin array of multiple well device disposed therein to conform to a predetermined shape, yet being rigid at room temperature.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is related to and claims the benefits of U.S.Provisional Patent Application No. 60/420,177 filed Oct. 21, 2002, thedisclosure of which is hereby incorporated herein by this reference.

BACKGROUND

[0002] 1. Field

[0003] The present invention relates to new classes of pixellated andconformal Modulated-Retro-Reflective (MRR) optical devices, includingmodulated corner-cube devices as well as modulated cat's eye devices.Instead of using a single, large-area modulator, the disclosed modulatorutilizes an array of individual pixels, which can be independentlycontrolled or modulated. The array need not be planar and can be formedto any shape as required by the optical design of the specific devicestructure.

[0004] 2. Description of Related Art

[0005] The novel classes of modulated retro-reflective (MRR) devicesdisclosed herein may be used for remote sensing, IFF (identification,friend or foe), laser communication links, and optical networks, such asoptical relay nodes.

[0006] The prior art includes conventional retro-modulation devicesusing bulk structures, as well as Multiple Quantum Well (MQW) baseddevices. See U.S. Pat. No. 6,154,299 by Gilbreath et al. of the NavalResearch Laboratory entitled “Modulating Retroreflector using MultipleQuantum Well Technology”, the disclosure of which is hereby incorporatedherein by reference. The prior art requires fabrication of the entireMQW structure and/or a pixellated array on a large common, planarsubstrate. For efficient link performance, a large aperture (forexample, in the 10 cm range) may be required. Such a relatively largestructure demands a very uniform deposition process so that the entiresurface has the same band structure and excitonic resonances, etc. Inaddition, the depth-of-modulation (optical contrast ratio) described inthe prior art are dramatically limited by the finite thickness of thethin MQW modulator (typically, 1 μm total thickness). This follows sincethe MQW component of the prior art is passed either once or twice by theoptical beam. By contrast, in accordance with one aspect of the presentinvention, the optical beam effectively multi-passes the MQW, since itis formed within a Fabry Perot cavity, so the effective number ofoptical transits can be in the range of 10 to over 100, depending on thedesign of the cavity Q. Moreover, such a planar structure cannot beflexed or made conformal to curved, generalized surfaces. This wouldnormally limit the ability to retrofit existing large, curved surfaceswith a large-area MRR device of such a construction. Moreover, thefield-of-view may be limited by such a planar structure, even in thecase of a large-area device. In addition, the prior art does notdescribe how to use a dual-mode device for the MRR structure (for bothphotodetection and optical modulation). Also, the prior art does notdisclose how to fabricate a device with Low Probability ofIntercept/Detection (LPI/LPD) in a common element, so that theretro-reflected beam is disabled prior to a successful handshakingprocedure (the prior art requires a stand-alone optical shutter toprevent a third party from interrogating the MRR). Finally, the priorart does not disclose a simple method of how to enable the MRR to dealwith multiple wavelength indication.

[0007] See, also, U.S. Pat. No. 6,455,931 to Hamilton, et al., which isowned by Raytheon Company of Lexington, Mass., the disclosure of whichis hereby incorporated herein by reference.

[0008] Utilizing a stand-alone shutter to prevent undesirableinterrogation of the MRR (as would be the case in the prior art) has adisadvantage since it does not allow the prior art devices to functionas a detector and a retro-modulator. Rather, separate detector andmodulator assemblies must be utilized. One of the features of thepresent invention is that while the MRR is in an off-state (that is,while it is effectively shuttered), it can also act as an efficientdetector.

[0009] The prior art also includes the use of retro-reflectors incommunication system. See “Design and analysis of a diffraction-limitedcat's-eye retroreflector” by Biermann, Rabinovich, Mahon and Gilbreath,Opt. Eng. 41(7), July 2002, pp 1655-1660, the disclosure of which ishereby incorporated herein by reference.

[0010] In accordance with one aspect of the present invention novelclasses of MRR devices are utilized for remote sensing, IFF(identification, friend or foe), laser communication links, and opticalnetworks, such as optical relay nodes and a novel fabrication technique.In terms of fabrication and in accordance with one aspect of the presentinvention, a technique is provided by which such devices can be robustlymanufactured so that they can conform to the surfaces upon which areplaced (planar, curved, etc. surfaces). The disclosed devices areespecially useful because they can be positioned on most curved surfaces(e.g., on the surface of a hemisphere, similar in layout to an eye of abee or fly). Hence, the overall device can thus accommodate a largefield-of-view (FOV) with an overall aperture much greater than thatprovided by existing fabrication techniques. The disclosed devices canalso withstand much greater vibration, acceleration and deformation,since the limiting dimension is now the individual pixel and not theoverall wafer dimension or aperture. Yet a further feature of thisinvention is that a variety of different devices can be fabricated withhigh yield, owing to the fact that all the pixels can be qualified priorto their self-assembly.

[0011] When the MRR devices disclosed herein are in an off state, theyare optically opaque to a optical probe, since the disclosed MRR devicesthen absorb the incoming light while performing a detection function.Also, since the disclosed MRR devices preferably utilize arrays ofindividual detectors/modulators, the ability to provide a shutteringmechanism which works on an individual detector/modulator basis, certainones of the detectors/modulators can be shuttered (in an off state)while one or more other detectors/modulators are modulating a probebeam.

[0012] The various possible advantages of this invention can besummarized by following (this list is not necessarily all inclusive nordo all embodiments of the invention necessarily enjoy all theseadvantages):

[0013] First, by using a pixellated modulator structure, the prior artcompromises between the modulator size for increased data rates and theMRR aperture for increased optical power can be overcome. This allowsthe design of the individual modulator pixel size for the desiredmodulation rate and the appropriate number of pixels to cover therequired optical aperture.

[0014] Second, a Multiple Quantum Well MQW asymmetric Fabry-Perotresonator structure can be conveniently utilized, which results inenhanced on-off contrast ratio and lower voltage operation compared to aconventional transmissive MQW modulator.

[0015] Third, the disclosed MQW pixels can operate as both modulatorsand photodetectors so that only the illuminated pixel(s) need beactivated for retro-modulation. This significantly reduces the powerdissipation of the MRR. As a result, a “smart” and more secureretro-reflector device can be used to communicate with an interrogatorin a selected portion of the FOV of the device, while disabling thedevice from being interrogated by undesirable third parties appearing inother portions of the FOV of the device. That is, once a handshakeprocedure has been completed, only the pixel(s) that need be activated(modulated) are activated (modulated), thereby restricting theretro-modulated return for that specified FOV, and disabling aretro-modulated return from being reflected to other parties. Thisfeature also tends to reduce the overall device power consumption of thedisclosed device.

[0016] Fourth, by using self-assembled pixel transfer technology, theMQW modulator pixels can be positioned on any surface in a predeterminedarrangement for optimum MRR optical performance. For example, thecat's-eye retro-reflector architecture, which uses a hemisphericalreflecting surface, can be readily realized using the disclosedconformal and pixellated MQW modulator structure. Such a structure canbe preformed, such as by casting or molding, and then the individualpixels can be applied thereto using self-assembled pixel transfertechnology. This hemispherical MRR structure will greatly enhance itsfield-of-view independent of its method of manufacture.

[0017] Fifth, by utilizing a flexible substrate, the entire retro-devicecan be conformally attached to a non-planar surface, such as thehemispherical surface mentioned above, thereby enabling the installationof the device onto an existing surface having an arbitrary curvature(e.g., curved platforms and structures) and also enabling effectiveinstallation of the device onto a surface which must be curved orconveniently is curved, such as a wing or airframe of an aircraft.

[0018] Sixth: Yet another advantage of using the disclosedself-assembled pixel transfer technique for the MRR is that differentMQW modulator pixels designed for operation at different wavelengths canbe positioned at alternate sites on the retro-reflector surface, henceallowing multi-wavelength MRR operation.

[0019] Seventh, by utilizing an Asymmetric Fabry-Perot resonatorstructure as an integrated detector/modulator, the detection/handshakestate of the device can be biased so that, in this mode, the device hasoptimal detection efficiency. In this mode of operation, nearly all theincident photons can be absorbed in a thin MQW layer. It turns out thatin this optimal detection mode, the net specular reflection from thedevice is also at a minimum. This follows, since the phasing of thebeams is such that the Fresnel reflection is canceled out by theFabry-Perot reflections. In this manner, the specular reflectivity ofthe MRR is effectively nulled out (all the photons are coupled into theasymmetric Fabry-Perot resonator), resulting in a near-zeroretro-reflective “glint” return from the structure (i.e., theretro-reflector is effectively an absorbing structure, with LPI/LPD).

[0020] Eighth, the disclosed apparatus can be used for opticalcommunication systems, wireless networks and links, remote sensor nodesand IFF scenarios. Such devices can be employed in myriad free-spaceapplications. It can also be utilized in terrestrial systems as part ofrapidly reconfigurable optical links for (i) in-factory transfer of datasuch as computer-aided design (CAD), (ii) video training, (iii)inventory control, (iv) manufacturing-on-demand information, (v) x-raydata or (vi) any other information requiring high bandwidths.

[0021] Ninth, the retro-modulator disclosed herein can also be used inroadside optical information kiosks for automobiles and other vehicles.By placing these potentially inexpensive devices in various locations onhighways and city streets (for example, traffic lights), the MRR canrelay a variety of traffic and entertainment information using a simpleoptical probe beam positioned on the car. Alternately, traffic controlpersonnel can use this technology to obtain detailed information aboutthe vehicle and its operating conditions by optical probing. In thiscase, the retro-modulator will be installed in the car. In yet anothervehicular related application, the optical probe is installed in thevehicle for use with optoelectronic-aided auto service to transfer datarequired to update some electronic components, for example, software orfirmware in the vehicle).

[0022] Tenth, in terms of a military application, the disclosed MRR isan ideal device for IFF applications where by simply probing a targetequipped with the retro-modulator and programmed with the correct code,the target can be easily identified. In addition, these MRRs can bemounted on missiles and/or torpedoes so that an optical beam can easilyrelay target and tracking information back at the launch site.

[0023] Eleventh, the disclosed MRR devices can also be used in airportand airborne traffic control applications for airplane accidentavoidance and aircraft identification information. Furthermore, there isa potential for long-range inter-satellite links as well asshorter-range shuttle-to-platform optical links using the disclosed MRRdevices. In these cases, the auto-alignment properties of the MRR,coupled with its monolithic, compact architecture, will greatly reducethe prime power requirements, cost, and weight requirements of thesystem over conventional optical links that employ sources andpointing/tracking subsystems. Finally, in the case of terrestrialapplications, adaptive optical techniques can be used to form up theinterrogation beam onto the MRR, thereby compensating for wavefrontdistortions along the path, as well as optimizing the link budget.

[0024] It should be noted that there are many aspects of this inventionand it will be apparent to those skilled in the art that not all of thefeatures, advantages and applications discussed above will necessarilybe applicable to all embodiments.

SUMMARY

[0025] In one aspect this invention involves new classes of pixellatedand conformal modulated-retro-reflective devices, including modulatedcorner-cube devices as well as modulated cat's eye devices. Instead of asingle, large-area modulator, the modulator consists of an array ofindividual “pixels,” which can be independently controlled or modulated.The array need not be planar and preferably can be formed to any shapeas required by the optical design of the specific device structure. Thepixels are in the form of small (≈100 μm) elements, such as multiplequantum wells (MQWs), which form the modulation structures.

[0026] In another aspect, this invention utilizes self-assemblyfabrication and/or transfer bonding techniques to realize these arraystructures. The pixels can be assembled into flexible substrates tocomplete the overall device, which can be conformed to the surface towhich it is to be attached.

[0027] In addition, the pixels need not be all the same. That is,different pixels can be resonant at different wavelengths, as anexample, so that a WDM device can be realized, with redundancy, ifnecessary.

[0028] In yet another aspect of this invention, Asymmetric Fabry-Perot(AFP) MQW structures are utilized as the pixellated elements. The AFPstructures can perform dual functions: they can act an optical modulator(low-voltage, high-depth-of-modulation and bandwidth) and as an opticaldetector (high efficiency, high bandwidth). Finally, refractive,reflective, and/or diffractive optical elements (in transmission orreflection modes) can be employed to complete the specific devicestructure. The result is a low-cost, rugged, conformal, and robustretro-modulation device with large field-of-view and largefield-of-regard, capable of high-bandwidth communication and IFF(identification, friend or foe) applications, with Low Probability ofIntercept/Detection (LPI/LPD).

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a schematic view of a conformal pixellated an AFP MQWmodulator structure in a cat's-eye retro-reflector configuration;

[0030]FIG. 1a is a schematic view of three AFP MQW modulator/detectordevices imbedded in a plastic substrate that forms a portion of aconformal pixellated structure of FIG. 1;

[0031]FIG. 1b is a detailed schematic view of a single AFP MQWmodulator/detector device disposed on a temporary substrate;

[0032]FIGS. 2a-2 e are side elevation views of a conformal pixellatedAFP MQW modulator structure 5 during various steps of a fabricationprocess;

[0033]FIG. 3 is a schematic diagram of a two-dimensional AFP MQWmodulator pixel array in plan view depicted with RF switches in eachpixel for single pixel-at-a-time activation;

[0034]FIG. 3a is a schematic diagram of another embodiment of atwo-dimensional AFP MQW modulator pixel array with an optical switch ineach pixel for single pixel-at-a-time activation;

[0035]FIG. 3b is a graph of the IN characteristics of an AFP MQWmodulator pixel operating as a photodiode;

[0036]FIG. 3c depicts pie or triangular-shaped planar elements which canbe easily deformed into a shape approximating a hemispherical shape;

[0037]FIGS. 3d and 3 e show an alternative optical arrangement forfocusing an incoming beam on a modulator/detector MQW device, thisalternative optical arrangement including an array of microlensesdisposed adjacent the array of modulator/detectors;

[0038]FIGS. 3f-3 h show how the lens sizes may be determined when lensesare used in the optical arrangement;

[0039]FIG. 4 depicts a multiple frequency embodiment of a pixellated AFPMQW modulator/detector structure;

[0040]FIG. 4a is a schematic view of eight AFP MQW modulator/detectordevices imbedded in a plastic substrate which form a portion of aconformal pixellated structure of FIG. 4;

[0041]FIG. 4b is a plan view of three AFP MQW modulator/detectordevices, each having a different frequency responsiveness, which threedevices define a single pixel;

[0042]FIG. 4c is a schematic representation of a reflecting embodiment;and

[0043]FIG. 5 is a schematic view of a conformal pixellated structure beutilized as a passive optical repeater.

DETAILED DESCRIPTION

[0044] A Conformal Modulated-Retro-Reflective Optical Device

[0045]FIG. 1 is sectional view through an embodiment of a conformalretro-modulator reflective optical device 10. The device 10 has an arrayof modulator/detector pixels 12 disposed along a surface 14. An opticalarrangement 20 (such as a lens) focuses an incoming optical beam 22 onone or more of the pixels 12 in the array. In this embodiment, thesurface 14 conforms to a hemispherical shape. As will be seen, thesurface 14 may be of any desired shape, including planar, but theoptical arrangement 20 does need to be able to deliver incoming light 22to selected pixels 12. In FIG. 1 the optical arrangement 20 is depictedas a single lens and a single lens can often suitably focus the beam ona geometric surface like the hemispherical surface 14 shown in FIG. 1.Other optical arrangements 20 may be utilized, including Fresnel lenses,holographic “lenses”, diffractive optical gratings, computer-controlledphase plates, multiple lens arrangements, and purely reflectivearrangements (see FIG. 4c). As such, the optical arrangement 20 may beplanar or nearly planar, if so desired. Additionally, the opticalarrangement 20 lens can be used in combination with lenslets affixed ordisposed at or near surface 14.

[0046] The lens or optical arrangement 20 may focus the incoming opticalbeam 22 on a single pixel 12 or the spot formed by the focussed beam mayfall on two or more adjacent pixels 12. As will be seen, each pixel maycomprise a single modulator 12 or it may comprise multiple modulatorseach sensitive to a different wavelength and/or it may compriseswitching devices.

[0047] The modulator/detector pixels 12 can both detect light fallingthereon and can selectively reflect or modulate the incoming light inresponse to electrical signals applied to the pixel. A suitable devicefor each modulator/detector pixel 12 in the array is a Multiple QuantumWell (MQW) device. MQW devices are well known in the art; typically theyhave alternating layers of different semiconductor materials (see FIG.1b), which may be formed, for example, by molecular beam epitaxy ormetal organic chemical vapor deposition. Typical semiconductor materialsused in MQW devices include, for example, GaAs, AlGaAs, and InGaAs. Thesemiconductor material with the lowest bandgap energy is known as thewell, while the semiconductor material with the higher bandgap energy iscalled the barrier. At wavelengths longer than a certain frequency,these semiconductor materials are transparent, while at shorterwavelengths (i.e. higher frequencies), they are opaque. At that“certain” frequency between transparency and opaqueness, thesesemiconductor materials exhibit a phenomenon known as “exciton.” Fornormal semiconductor materials at room temperature, the exciton featureis not particularly distinct. But in a MQW device, the exciton featurebecomes much more distinct and its associated wavelength (correspondingto the certain wavelength noted above) becomes a function of both thethicknesses of the semiconductor layers and of an applied electricfield.

[0048] If the electric field intensity is modulated, then the MQWdevice, in an appropriate optical arrangement, will reflect light,intensity modulating the reflected light according to the intensity ofthe applied electric field.

[0049] The modulated retro-reflective (MRR) device 10 of the presentinvention can preferably be conformally shaped and attached onto anarbitrarily shaped surface. The MRR device can be conveniently made froman array of MQW devices arranged as an array of pixels 12. A MRR devicein accordance with the present invention can be conveniently placed ontoexisting structures, whose constraints may otherwise negate thepossibility of using prior art MRR/MQW devices, which are typically of aplanar, pyramidal, or spherical configuration. The overall device 10structure of the present invention can be made to be concave, convex,etc. and can be shaped to conform to the desired surface to which it isto be attached. A key advantage of this invention is that a much greaterfield-of-regard (FOR) can be realized, since an entire hemisphere can becovered with a large MRR array, for example, in a cat's eyeconfiguration.

[0050] The MRR 10, which includes an array of optical modulating devices12 of the type preferably having a retro-reflecting surface, allows anincoming CW optical beam from the transmitter to be simultaneouslymodulated and reflected back to the transmitter/receiver on the sameoptical path 22.

[0051] An embodiment of a MRR 10 is shown in FIG. 1 in which thehemispherical surface 14 of a cats-eye configuration is populated withan array of reflective MQW modulator pixels 12 mounted in a flexible ordeformable substrate, sheet or support layer 16, such as a polymer,including thermo-setting materials, preferably using self-assembly ortransfer bonding pixel transfer technologies. Preferably, the flexibleor deformable material is relatively plastic at temperatures above roomtemperature, thereby allowing the substrate, sheet or support layer 16and the array of modulator and/or detector pixels 12 embedded therein toconform to a hemispherical configuration (for example), while beingrelatively rigid at room temperature.

[0052]FIG. 1a is an enlarged view of a few reflective MQW modulatorpixels 12 supported by the flexible or deformable substrate 16 whileFIG. 1b shows a single reflective MQW modulator 12 disposed on aremovable substrate 120. The array of reflective MQW modulators 12 ispreferably a two dimensional array and the reflective MQW modulators 12are formed in as thin array of materials preferably using conventionalsemiconductor processing technologies in a flexible or deformable sheet16. The individual MQW devices are preferably very thin and preferablyhave a thickness in the range of 1 to 5 μm. The sheet 16 itself, whichincludes a relatively thick layer of a flexible or deformable material,has an overall thickness which is sufficient to mechanically support theMQW modulators 12. Typical thicknesses of the flexible or deformablesheet 16 will depend upon the material used and are apt to fall in therange of 5-100 μm. At this range of thicknesses, the sheet 16 bearingthe array of reflective MQW modulators 12 should preferably be able tosupport itself.

[0053] The incoming CW beam from a transmitter 24 is represented byreference numeral 22 in FIG. 1. The beam may be focussed on anindividual one or individual ones of the reflective AFP MQW modulatorpixels 12 in the array by means of optical arrangement 20. The incomingCW optical beam 22 from the transmitter 24 is simultaneously modulated(by the modulator pixel(s) 12 which it impinges and which are suitablyelectrically biased) and reflected back to the receiver on the sameoptical path as beam 22.

[0054] In FIGS. 1a and 1 b, the reflective MQW modulators 12 have ashape which approximates a truncated cone. The individual reflective MQWmodulators 12 are formed by a series of semiconductor layers 125 ofAlGaInAs and GaInAs, for example. A partially reflective frontal mirror121, which may be formed by an InAlGaAs/InAlAs Distributed BraggReflector (DBR), and a reflective metal back mirror 122, which may beformed of platinum, and therefore may also serve as a p-type contactmetalization. Alternatively, a dielectric medium or a DBR can alsoservice as the back mirror. Of course, the two mirrors 121, 122 impartan Asymmetrical Fabry-Perot (AFP) configuration if the distance betweenthe two mirrors 121, 122 is controlled as is standard with Fabry-Perotdevices. The AFP MQW modulators 12 may be designed to operate at aneye-safe 1550 nm and the distance between the two mirrors is selectedaccordingly. Of course, other frequencies of operation may also beutilized. In FIG. 1b a single MQW modulator 12 is shown on an InPsubstrate 120. The MQW devices 120 are formed as an array of devices 12on substrate 120. After embedding devices 12 in polymer 16, thesubstrate 120 is removed.

[0055] As can be seen from FIG. 3, there are conductive pathways,channels or electrodes 18, 19 in sheet 16, which channels or electrodesare preferably conductors of a suitable metal and which attach to thetruncated cone-like reflective MQW modulators 12 at their contacts 124and 126. The conductive pathways, channels or electrodes 18 in sheet 16are preferably formed in a matrix configuration using conventionalsemiconductor manufacturing technologies and, in use, are used tocontrol the individual reflective MQW modulators 12 in the array. Thereare typically two conductive pathways, channels or electrodes 18, 19 insheet 16 coupled to each reflective MQW modulator 12 in the array. Theconnection to the electrodes 18, 19 from external driver or controlapparatus may be accomplished through the use of p-type or n-typesemiconductor material or other suitable techniques. Whether all theseconductive pathways, channels or electrodes 18, 19 are made accessible,at a connector, for example, as a matrix of conductive pathways,channels or electrodes 18 or whether switching techniques are utilizedto reduce the number of conductors which need be brought out from theMRR shown in FIG. 1 is a matter of design choice. The same is true forthe level at which the conductive pathways, channels or electrodes 18 insheet 16 are formed. Recall that the conductive pathways, channels orelectrodes 18 in sheet 16 attach to the contacts 124, 126 of eachmodulator 12. The conductive pathways, channels or electrodes 18 can beformed using semiconductor processing technologies and are convenientlyseparated from one another using a dielectric material, such as silicondioxide or silicon nitride, which is also conveniently formed usingsemiconductor processing technologies. As such, using semiconductorprocessing technologies, the conductive pathways, channels or electrodes18, 19 and the dielectric material will be arranged in layers as isconventional using that technology.

[0056] The conductive pathways, channels or electrodes 18, 19 can bedisposed closer to surface 121 or to surface 122 of the modulators 12,and may be arranged to be immediately adjacent surface 14 withdielectric material being utilized a crossover point 21 where theconductors 18 in the matrix cross over one another. Arranging theconductive elements 18, 19 closer to surface 14 can make for convenientconnection to the conductive pathways or channels 18 in sheet 16 whilearranging the conductors 18, 19 closer to surface 121 can allow themodulators 12 to be more densely packed in sheet 16. The use ofswitching techniques to reduce the number of conductors which need bebrought out from the MRR 10 will also tend to increase the spacing ofthe modulators 12 from one another. Since a tightly packed array ofmodulators 12 will be advantageous in many applications, certainengineering tradeoffs must be made when deciding how to layout theconductors 18, 19 in sheet 16 and in deciding whether addingsemiconductor switches in sheet 16 make sense.

[0057] The supporting flexible or deformable substrate 16 is depicted inFIGS. 1 and 1a as being about the same thickness as modulators 12;however, this is for ease of illustration only. In fact, the supportingflexible or deformable substrate 16 has a thickness sufficient toprovide sufficient mechanical support to sheet 16 in practicalapplications of this invention.

[0058] An aspect of this invention is that the modulator function ispixellated, so that each MQW device 12 in the array of such devices hasits own Field-of-View (FOV), which called a sub-FOV herein and which canbe independently controlled (e.g., modulated or not, or, differentpixels can be modulated with different information). This allows theoverall capacitance of the entire device to be minimized, since theencoding need only be imposed onto the modulator(s) 12 of choice. Inaddition, since only the desired sub-FOV is modulated, otherinterrogators outside this sub-FOV would not receive back a modulatedretro-return, if so desired. In addition, the use of a pixellated arrayof modulators will enable the overall device to function even if one ofthe pixels becomes inoperative, whereas devices with a single, largemodulation element would become totally inoperative if the modulatorbecomes inoperative.

[0059] The modulation elements 12 are preferably made from semiconductormaterials, such materials being preferably implemented as MWQ devices,which, in turn, are preferably arranged in an AFP optical configuration.Moreover, other MQW material systems are known, including polymers andorganic materials, etc. which can alternatively be used, suchalternative materials also being used preferably in an AFP opticalconfiguration. In addition, the substrate need not be lattice-matched tothe modulation elements, enabling a wide variety of substrate materialsto be used, which can be flexible, as well as transparent to otherportions of the spectrum, if desired. Operation can be in the opticalspectrum, as well as in the RF and mm-wave portions of the spectrum, byscaling disclosed embodiment to those frequencies.

[0060] In a preferred embodiment, the modulation elements 12 are in theform of Asymmetric Fabry-Perot (AFP) resonator based MQWs. This class ofstructure has the ability of encoding the desired modulation signal withrelatively low voltage (owing to the Q-enhanced resonator). Moreover,the depth-of-modulation, as well as the “dark state” (or, contrastratio) can be very high. The AFP modulator also has the feature that inthe “off state,” the reflectivity is at a minimum (near zero), so thatinterrogation by an undesirable third party will result in a near-zero“glint” return, enabling LPD/LPI scenarios to be achieved. This is apotentially important feature of the present invention. In the prior artan additional shutter has been placed in front of the modulators inorder to enable zero off-state return.

[0061] Due to the use of pixel transfer techniques, the need forlattice-matched substrates can be obviated, enabling more generalclasses of substrates to be employed using various modulation elements(either reflective or transmissive elements) 12. A variety of pixeltransfer techniques can be employed, including (1) self-assembly orfluidic transport of “pixels” with modulation capability (e.g.,solid-state MQW or polymer-based optical/RF modulator elements) ontoembossed/etched/molded substrates; and (2) transfer of modulator arraysusing etching/liftoff/transfer-bonding processing onto polymer/plasticsurfaces.

[0062]FIGS. 2a-2 e schematically show steps which may be employed inorder to make a conformal retro-modulator using a wafer-scale pixeltransfer technique. This fabrication process involves:

[0063] (i) forming and interconnecting a planar two-dimensional array ofmodulator pixels 12 on a suitable substrate 120 (see FIGS. 1b and 2 a);

[0064] (ii) embedding the array of prefabricated and interconnectedmodulator devices 12 into sheet 16 (see FIG. 2(b));

[0065] (iii) segmenting the support layer, as needed, for 2-D or 3-Dcurvature (see FIG. 2(c)); (iv) selectively removing the growthsubstrate 120 (see FIG. 2(d)); and

[0066] (v) shaping the sheet 16 into a hemispherical conformal structure(see FIG. 2(e)).

[0067] For more information regarding the manufacturing techniquesutilizing flexible substrate, reference may be made to U.S. Pat. No.6,455,931 issued Sep. 24, 2002.

[0068] An individual MRR 10 employs preferably an array of pixellatedmodulators 12 (as opposed to a single modulator 12), enabling the systemto address large fields-of-view (FOV) and large fields-of-regards (FOR).By using pixellated modulators 12, the modulation bandwidth can beoptimized by selecting the appropriate modulator size, and hence,capacitance, since the modulation speed is RC limited.

[0069] Moreover, a “smart” MRR 10 can be realized, since individualmodulation elements can be selectively engaged (after appropriatehandshaking) so that specific FOV can be addressed, while the remainderof the FOV is not activated, leading to lower power requirements, and toLPI/LPD operation.

[0070]FIG. 3 shows a two-dimensional modulator 12 pixel array in whichthe array is sequentially scanned with a sensing voltage on conductors18, 19. This array is depicted with only nine modulators 12 for ease ofillustration only—practical embodiments will likely have very manymodulators 12. The dual-mode modulation/photodetection capability of theASFP modulator 12 pixels in the array allows sensing which pixel(s), ifany, is/are activated by the interrogating optical beam 22 (see FIG. 1).Once the activated pixel(s) is/are detected, the modulation signal issubsequently only applied to that/those pixel(s) using RF switches(preferably MEMS switches) 30, 32, as shown in FIG. 3 or opticalswitches 30 as shown in FIG. 3a. The interrogating optical beam may havea code applied thereto before shifting to an unmodulated (CW) form. Aprocessor 31 (see FIG. 1) associated with device 10 can be utilized totest the code supplied by the interrogating beam 22 to ensure that thereceived code is “correct”. This allows the device 10 to respond only tointerrogating beams 22 from a known source. Once the correct code isidentified, then the device 10 communicates with the transmitter 24 bymodulating and reflecting the received unmodulated beam 22. Theprocessor 31 is coupled with each modulator 12 in the array eitherdirectly or via switches 30.

[0071] Since the device 10 has a plurality of pixels 12, it cancommunicate with a plurality of transmitters 24 at a given time.

[0072]FIG. 3a shows a two dimensional modulator 12 pixel array in whichthe array is sequentially scanned with a sensing voltage on conductors18, 19. This embodiment differs from tile embodiment of FIG. 3 by theaddition of optically activated switches (OAS) 30, which may be providedby phototransistors or optically controlled MEM switches, each of whichswitch 30 is connected in series with an associated modulator 12.

[0073] The addressing scheme for the array modulators 12 shown in FIG.3a works as follows. Assume that initially the MMR 10 is in a quiescentstate with no voltage applied to the individual modulator 12 pixels.This means that all row (x_(n)) and column (y_(m)) electrodes 18, 19 areat zero potential. The column electrodes 18 are scanned, preferablysequentially, (for m=1 to M) to detect any sensing current resultingfrom the photoactivation of a pixel 12, 30. For example, let us assumethat the pixel x₁,y₁, is photoactivated by an incoming probe laser 22focussed on it. The OAS 30 in this pixel is switched on as a result ofphotoactivation by the incoming beam 22. A sensing photocurrent issensed in the y₁ electrode even with no bias applied to the modulator 12due to its built-in pin diode (see FIG. 3b). In order to determine therow electrode 19 to which the activated pixel 12, 30 belongs, the rowsx_(n) (for n=1 to N) are scanned, preferably sequentially, with a smallnegative voltage. As shown in the I-V characteristics of the pinmodulator operating as a photodiode (see FIG. 3b), for row electrodeswith the photoactivated switch OAS 30 turned on, the small negativephotodiode bias results in a reduction of the sensing current from thezero-bias value, while for row electrodes where no pixel isphotoactivated, the OAS 30 is switched off and no change in the sensedphotocurrent is detected. Thus, the photoactivated pixel 12, 30 (in thiscase pixel x₁ y₁) is determined. If the photoactivated pixel is tuned onby a “friendly” probe beam (as determined by receiving a properhandshaking optical pulse sequence), a modulating voltage waveform maybe applied to the corresponding row electrode for that particular pixel,which has its column electrode at zero potential (since itscorresponding OAS 30 has been turned on and the small negative voltageapplied above has since been removed), if it is desired to communicatewith the transceiver 24 sending beam 22. If, on the other hand, thephotoactivated pixel 12, 30 is probed by an “unfriendly” source, thehandshaking sequence fails and a voltage V_(o), which is the zeroreflection bias for the affected pixel, is preferably applied to thecorresponding row electrode. With a V_(o) bias applied, no light isretroflected to the unfriendly optical transceiver, resulting in a zeroglint return.

[0074] The column electrodes keep scanning (preferably sequentially) inorder to sense any new potential photocurrent resulting from thephotoactivation of another pixel 12, 30. Assume, for the moment, that athird column y₃ is determined to have some sensing current. Again, therow electrodes x_(n) (for n=1 to N) are scanned to determine the newlyphotoactivated pixel by the same scheme described above (the reductionof the sensing current in the photoactivated row by the application of asmall negative voltage). Assume that a pixel x₃y₃ is the newlyphotoactivated pixel with a status of “unfriendly” as determined by afailed handshaking sequence. As described above, a voltage V_(o),corresponding to the zero reflection bias, is applied to a third rowelectrode x₃ with the column electrode y₃ remaining at a zero potential.Now assume that yet another pixel 12, 30 (in this case pixel x₁y₃) issensed as being photoactivated by another unfriendly source. If theunfriendly probe at x₃y₃ still persists, pixel x₁y₃ will now see themodulated waveform if corrective action is not taken. This is, ofcourse, undesirable. Consequently, the voltage applied to row electrodex₁ will temporarily change to V_(o) corresponding to the zero reflectionbias so long as the unfriendly probe at x₁y₃ persists. The chance ofthis scenario happening is N/N·M or 1/M. Thus if the array is a 100 by100 array of pixels 12, 30, these scenario should be rather unlikely tooccur.

[0075] Now assume that pixel x12y₂ is sensed as being photoactivatedwith a status of “unfriendly”. The voltage applied to column electrodey₂ can now be changed from zero to a waveform complementary to themodulating waveform on row electrode x₁ with an added dc bias of V_(o).Thus, the difference between the waveforms on row electrode x₁ andcolumn electrode y₂ applied to pixel x₁y₂ is simply V_(o), whichcorresponds to the zero reflection bias, for the duration of thisunfriendly probe. As such pixel x₁y₂ will provide zero glint return tothe unfriendly probe.

[0076] Finally, assume that pixel x₂y₂ is sensed as being photoactivatedwith a status of “friendly”. Since now the complementary waveform isbeing applied to the column electrode y₂, a constant voltage V_(o) isapplied to electrode x₂ to result in the original modulating waveformbeing applied to the modulator 12 in this pixel.

[0077] Thus, this addressing scheme provides a very simple yet effectivescheme for addressing the MRR 10 pixels. Note that this is done withonly a total number of addressing electrodes equal to the sum of thenumber of rows and columns (N+M). The introduction of an OAS 30 in eachpixel which is associated with (and connected in series with) anassociated modulator 12 in each pixel, allows for the OAS 30 to bephotoactivated using the same probe light used for retromodulation ofthe modulator 12 in the pixel. If electrical switches are substitutedfor the OASs 30, then at least one control electrode would be needed foreach such switch 30, resulting in the addition of M−N additionalelectrodes to the addressing arrangement shown in FIG. 3a. The additionof such additional electrodes is clearly not desirable and thus it ispreferred that switches 30 be optically activated.

[0078] The switching schemes described with reference to FIGS. 3 and 3ahave been based on the assumption that the array is a rectangular arrayof size M×N. This analogy works well if the array is disposed on a flatsurface or if it is disposed on a surface which is easily formed from aflat surface (such as a cylindrical surface) or can be formed without alot of deformation of the flat surface (such as a gently rollingsurface). However, this analogy breaks down on a hemispherical surfacesince deforming a flat surface causes overlapping folds to occur informerly flat surface. However, pie or triangular, shaped pieces can bemade to assume close to a hemispherical shape, such as the pie ortriangular-shaped pieces used to make certain hats, such as baseballcaps.

[0079]FIG. 3c shows four pie or triangular-shaped, originally planar,elements 35 which are deformed, as shown, into a shape approximating ahemispherical shape and joined at seams 37. The individual elements 35may be made as previously described with reference to FIGS. 2a-2 e or astaught by U.S. Pat. No. 6,455,931. The elements 35 depicted in FIG. 3ceach have an array 36 of modulator/detector pixels 12 which can beaddressed using the schemes discussed with reference to FIGS. 3 and 3a,with appropriate modification to reflect the fact that individualelements 35 are more or less triangle-shaped and thus the lengths andorientations of the rows and/or column conductors 18, 19 need beadjusted accordingly. Each element 35 can have its own set of conductors18,19 (for addressing devices 12) which may be embedded along with themodulator/detector devices 12 in support layer 14, which is preferablydeformable.

[0080] The term “hemispherical” as used herein is intended to include ahemispherical-like surface formed from originally planar elements 35.

[0081]FIGS. 3d and 3 e show an alternative optical arrangement 20 forfocusing an incoming beam 22 on a modulator/detector MQW device 12. Inthis embodiment, the optical arrangement 20 includes an objective lens201 and an array 205 of microlens (or lenslets) 202. The objective lens201 is placed at or near the opening in the hemispherical surface 14.The hemispherical surface 14 is covered by the microlens array 205 witheach microlens 202 being associated with (and centered on) a differentmodulator/detector 12. The use of microlens (or lenslets) 202 isparticularly important if the MQW devices 12 are in an AFP opticalconfiguration since the light impinging a Fabry Perot modulator shouldbe as close to collimated as is reasonably possible to obtain an optimummodulator contract ratio.

[0082]FIGS. 3f-3 h show how the lens sizes may be determined. FIG. 3fshows an objective lens 20 for the embodiment of FIG. 1, for example.FIG. 3g shows an optical arrangement 20 which comprises an objectivelens 201 and microlens 202 configuration for the embodiment of FIGS. 3dand 3 e, while FIG. 3h shows a detail of the configuration of microlens202.

[0083] A Multiple Frequency Embodiment

[0084] The previously discussed embodiments have had a single AFP MQWdevice 12 for each pixel. The implicit assumption has been that thedevices 12 all operate on a common frequency. In fact, the AFP MQWdevices can be arranged in groups wherein each AFP MQW device 12 isresponsive to a different frequency of laser light. In that case, eachgroup of AFP MQW devices 12 constitutes a pixel.

[0085] In FIG. 4, the AFP MQW devices 12 are grouped in threes, withthree MQW devices 12 comprising a pixel. If the AFP MQW devices 12 ofFIG. 4 are of the same size as the AFP MQW devices 12 of FIG. 1, thenthe pixel size is, of course larger, and the optical arrangement 20 isthus adapted to throw a spot 25 (see FIG. 4b) of focused laser light onone pixel of three AFP MQW devices 12. An AFP MQW device is responsiveover a very short frequency range (about 10 nm in terms of wavelength).Thus, the AFP MQW devices in each group or pixel need not be widelyspaced in terms of their frequency responsiveness and thus the opticalarrangement 20 can utilize either a single lens or, as shown by FIGS. 3dand 3 e, an objective lens 201 plus an array 205 of microlenses 202 andstill focus the incoming beams 22 of different frequencies on thepixels. If the frequencies are relatively widely spaced (for example:850, 1300 and 1550 nm center wavelengths), then a purely reflectingrather than a catadioptric or refracting system could be utilized (seeFIG. 4c) or multiple lenses could be used in order to minimize chromaticdispersion. As such, the objective lens 201 may be implemented as aseries of lenses in order to compensate for chromatic dispersion.

[0086]FIG. 4a is a more detailed side section view of a few of the AFPMQW devices 12 with an indication of the particular frequency (in termof wavelengths: λ₁, λ₂, and λ₃) to which each is responsive. Three AFPMQW devices 12 make up a pixel, but instead of a linear arrangement ofthree AFP MQW devices as schematically depicted in FIG. 4a, in actualitya pixel is preferably comprised of three AFP MQW devices 12 disposed ina triangular pattern, when viewed in plan view, as shown by FIG. 4b.

[0087] The “color” or frequency of the laser light can be used, ifdesired, to convey information such as the source of the data or itsimportance.

[0088] Also, the use of multiple colors, such as is found in fiber opticWavelength Division Multiplexing (WDM) technology, can be used toincrease the total throughput (data rate) of the MRR.

[0089] A MRR Optical Repeater

[0090] The MRR 10 with an associated processor 31 and a back planeswitch 28 can be utilized as an optical repeater or relay point. SeeFIG. 5. MRR 10 can receive a message from one transmitter 24 a on beam22 a and then relay that message along to one or more othertransceiver(s) 24 b by modulating the beam(s) 22 b from transceiver(s)24 b and reflecting it (or them) back to transceiver(s) 24 b. This dataexchange can occur simultaneously or sequentially. For example, assumethat transceiver 24 a is the source of a message to be passed to atleast one remote transceiver 24 b. Transceiver 24 a initiates matters bycontacting MRR 10 by sending a probe beam 22 a and going through ahandshaking sequence whereby processor 31 confirms that transceiver 24 ais “friendly.” Transceiver 24 a sends a message to the processor 31 viaback plane switch 28 and processor 31 which can be stored, for example,in a cache memory 33 associated with processor 31. The message wouldpreferably include routing information indicating the stations(transceivers) permitted to receive the message, whether the message maybe stored for later delivery, whether a receipt acknowledgement shouldbe sent back to station 24 a, how long the message is to remain in thecache 33 before being cleared, etc.

[0091] Assume that transceiver 24 a sends a message to be relayed totransceiver 24 b. If transceiver 24 b is “on-line”, that is it has gonethrough a handshaking sequence with the MMR 10 and processor 31 already,then the incoming message from transceiver 24 a can be directly routedto the particular pixel or pixels 12 in communication with transceiver24 b directly through back plane switch 28. If transceiver 24 b is noton line, then the message can be stored in a cache 33 associated withprocessor 31 for later delivery.

[0092] Multiple communication paths can transit the device of FIG. 5.Thus, different elements 12 can be modulated with differentretro-information. This can result in a more robust network node as wellas to an optical interconnect/relay device, since different FOVs withinthe overall FOR can be addressed with independent information. This canlead to an optical interconnection device, as well as a device withLPI/LPD, since other FOV elements need not be activated.

[0093] In terms of fabrication, the devices 12 in each pixel can have adifferent and distinctive shape so that fluid transport self-assemblytechniques can be used to place the individual devices into properplaces in a molded structure, for example.

[0094] In FIG. 5, each AFP MQW device 12 has it own connection 224 toback plane switch 28 and a common connection 226 shared by all pixels12. This is an alternative connection scheme to that disclosed by FIGS.3 and 3a. The primary disadvantage of this scheme is that the number ofconnections to switch 28 increases dramatically compared to the X,Yschemes of FIGS. 3 and 3a. For example, if the pixels are arranged in a100×100 array, the schemes of FIGS. 3 and 3a call for 100 columnelectrodes and 100 row electrodes (or 200 total connections), while thescheme of FIG. 5 calls for 10,000 connections, which would likely to beconsidered to be unwieldy by most persons skilled in the art. On theother hand, the scheme of FIG. 5 does have certain advantages whenassumptions are made about communicating with multiple pixels on acommon row or a common column. So, as in many things, there is anengineering trade off to be made and that which is preferred will dependupon the circumstances. One possibility would be to divide a large arrayinto a number of smaller arrays, which each smaller array having its ownX,Y addressing scheme (like FIGS. 3 or 3 a). For example, if a 100×100array is viewed as sixteen 25×25 pixel arrays, then the number ofconnections would be fifty per subarray or 800 total connections.Moreover, the subarrays need not be square. Triangularly shapedsubarrays of pixels can certainly be formed (as could other shapes).Such triangularly shaped subarrays can be formed on wafers which are, aswill be seen, arranged in a hemispherical shape like a geodesic dome.

[0095] Geodesic Hollow Structure Embodiment

[0096] Another embodiment of device 10 involves an array or arrangementof sub-wafers, with each sub-wafer comprised of a monolithic array ofpixels (with each pixel individually addressed for detection/modulationfunctions or addressed in an X,Y scheme, as desired). As an example,each sub-wafer may consist as an array of 100 total pixellated devices12 (say, ten by ten pixels), with all the electrical connections to theindividual pixels included in the sub-wafer chip. An ensemble of thesesub-wafers, in turn, is used to form the entire retro-modulator device10. One such arrangement can be an ensemble of polygons (e.g.,triangles), of dimensions of about 1 mm on a side, with each triangularwafer chip containing a number of 100 μm pixels. These triangularsub-wafers can be assembled into an approximate cat's eyeretro-reflector by employing a geodesic hemispherical dome as a housing.The geodesic dome consists of an array of polygons arranged so that eachedge of the polygons meets the adjacent edges of the neighboringpolygons so that the overall structure approximates the shape of asmooth hemisphere. Each triangular (or, polygon, in general) sub-waferis placed on the inner surface of the geodesic hemisphere so that itsdimensions are exactly equal to the geodesic structure. In this manner,an array of flat triangular wafers can have an overall large shape thatapproximates a hemisphere. This structure enables one to fabricate aretro-modulator device 10 with fewer overall assembly steps (since agiven triangular wafer contains many pixels), and, thus fewer individualconnection points (since all the connections within each sub-wafer areresident on that given chip). Since the overall device may have a smalleffective optical aperture, d (say, about 1 mm to 1 cm), then thediffraction effects (lambda/d) may be on the same order as the penaltypaid due to the segmented geodesic device relative to a smoothhemispherical structure.

[0097] Additional Comments and Modifications

[0098] The disclosed structures enable one to realize a modulationcapability with large depth-of-modulation at low modulation voltages,with a very efficient dark (i.e., off) state. This further reduces theoverall power consumption of the device. The individual pixels of thisdevice function both as an optical modulator as well as an opticaldetector. It may not be obvious to one skilled in the art of opticalmodulators (e.g., spatial light modulators, beam control devices, etc.)that a modulator can also function as a detector. Moreover, it may notbe obvious to one skilled in the art of optical detectors (say, opticalreceiver design and photodetection) that a detector can also function asan optical modulator. Furthermore, it may not be obvious to one skilledin the art that, in accordance with one aspect of the present invention,the necessary condition to electrically bias the detector for maximumdetection performance (i.e., to enable all the photons incident on thedevice to interact with the MQW) is precisely the same electrical biasrequired to optimize the contrast ratio when using the device as anoptical modulator (i.e., provide for an “off state” with zeroretro-reflectance).

[0099] The use of self-assembly techniques also enables one to fabricatedevices with different wavelength structures in a planar architecture,novel multi-wavelength structures (i.e., stacked MQWs), etc. Moreover,this fabrication process can enable rapid upgrading of the devices,since new MQWs can be retro-fitted into existing substrate structures.Finally, this process, can enable high-yield devices to be realized,since the individual pixels can be tested and qualified prior to theirself-assembly step, thereby optimizing the probability that the finalstructure will be 100% functional.

[0100] It should be noted that several different device methodologiescan be realized in terms of pixel size relative to the smallestresolvable FOV. In one case, the dimension of the modulation pixels canbe chosen so that each resolvable sub-FOV is addressed by a single pixelelement (on the order of 100 to 500 μm). In another case, several pixelscan be used to service a given sub-FOV. In the latter case, themodulation signal can be multiplexed among the group of pixels and/ordifferent pixels within this group can be designed to service differentwavelengths, so that the MRR device 10 can be more robust or have ahigher data transfer rate using WDM technology.

[0101] The MRR structure 10 can either be placed in a concave surface,over a convex surface to service a very large field-of-regard (similarto the eye of a fly or bee), or conformal to a general surface (such asan airborne platform, a satellite, an automobile, etc.) or it can remainflat. The basic device can be fabricated using conventional opticalcomponents as well as diffractive optical elements. In the former case,lenses or mirrors can be employed for cat's eye or corner-cube MRR,whereas in the latter case, diffractive (reflective or transmissive)elements can replace conventional optics. Finally, the overall fillfactor of the device can be optimized by employing a lenslet array (ordiffractive optical equivalent) so that most of the incident beam over agiven FOV is focused onto a given pixel. In this manner, the insertionloss of the MRR device 10 can be minimized.

[0102] The MQW devices 12 are referred to both as modulators and asdetectors herein. These devices can function as either a modulator or adetector depending on how they are biased, and for most embodiments itis believed that the operational flexibility will dictate that devices12 be able to function as both modulators or detectors by changing theirelectrical bias. However, some practicing the present invention maychoose to operate certain ones (or all) of the devices 12 as detectorsin some embodiments and/or choose to operate certain ones (or all) ofthe devices 12 as modulators in other embodiments.

[0103] Having described this invention in connection with a preferredembodiment, modification will now certainly suggest itself to thoseskilled in the art. As such, the invention is not to be limited to thedisclosed embodiments except as required by the appended claims.

What is claimed is:
 1. An optical apparatus comprising: a twodimensional array of modulator and/or detector pixels embedded in aflexible or deformable body, the modulator and/or detector pixelsresponding to applied electrical signals to modulate and reflect lightimpinging the modulator and/or detector pixels; and an opticalarrangement for directing an incoming optical beam from an opticaltransmitter onto a selected one or ones of said modulator and/ordetector pixels in said array and for returning light which is modulatedand reflected by said pixels to an optical transmitter from which theincoming beam was directed to the optical arrangement.
 2. The opticalapparatus of claim 1 further including electronic equipment for sensingwhen light impinges on said pixels and for supplying data signals tosaid pixels to cause said pixels to reflect the impinging light inaccordance with the data signals applied thereto.
 3. The opticalapparatus of claim 2 and an associated electrical matrix for connectingthe modulator and/or detector pixels in said array to the electronicequipment.
 4. The optical apparatus of claim 1 wherein the array ofmodulator and/or detector pixels is an array of Asymmetric Fabry-PerotMultiple Quantum Well devices.
 5. The optical apparatus of claim 4wherein the optical arrangement is a lens which focuses the incomingbeam onto said selected one or ones of said modulator and/or detectorpixels in said array.
 6. The optical apparatus of claim 5 wherein theflexible or deformable body is a thermosetting material.
 7. The opticalapparatus of claim 6 wherein the flexible or deformable body is disposedin a hemispherical configuration.
 8. The optical apparatus of claim 1wherein the flexible or deformable body has a sheet-like polymer supportelement in which the two dimensional array of modulator and/or detectorpixels are embedded.
 9. The optical apparatus of claim 1 wherein theplastic support element is relatively plastic at temperatures above roomtemperature, thereby allowing the plastic support element and the arrayof modulator and/or detector pixels embedded therein to conform to apredetermined shape, while being relatively rigid at room temperature.10. The optical apparatus of claim 1 wherein each modulator pixelcomprises a plurality of AFP MQW devices.
 11. The optical apparatus ofclaim 1 wherein each modulator pixel comprises at least one AFP MQWdevice and at least one optically activated switch connected in serieswith the at least one AFP MQW device.
 12. The optical apparatus of claim1 wherein each modulator pixel comprises at least one AFP MQW device andtwo optically activated switches connected in series with the at leastone AFP MQW device.
 13. The optical apparatus of claim 1 wherein themodulator and/or detector pixels are arranged in an array separated bypixel addressing electrodes arranged in a matrix, each modulator pixelhaving a pair of contacts for connection to separate adjacent addressingelectrodes.
 14. A passive optical repeater comprising: a two dimensionalarray of modulator and/or detector pixels disposed in a predeterminedconfiguration, the modulator and/or detector pixels responding toapplied electrical signals to modulate and reflect light impinging themodulator and/or detector pixels; an optical arrangement for directing afirst incoming optical beam from a first optical transmitter onto afirst selected one or ones of said modulator and/or detector pixels insaid array and for directing a second incoming optical beam from asecond optical transmitter onto a second selected one or ones of saidmodulator and/or detector pixels in said array, the first incomingoptical beam being modulated with data; and an electronic apparatus fordetecting the data on the first incoming optical beam and for modulatingthe second incoming beam at said second selected one or ones of saidmodulator and/or detector pixels in said array using said data; whereinthe second incoming beam is reflected at said second selected one orones of said modulator and/or detector pixels via the opticalarrangement back to said second optical transmitter.
 15. The passiveoptical repeater of claim 14 wherein the two dimensional array ofmodulator and/or detector pixels is disposed in a hemisphericalconfiguration.
 16. The passive optical repeater of claim 14 wherein theelectronic apparatus includes a back plane switch arrangement and aprocessor.
 17. The passive optical repeater of claim 16 wherein theelectronic apparatus includes a cache memory for temporarily storingreceived data from one source, the electronic apparatus modulating abeam from another source with the data stored in the cache.
 18. Anoptical relay apparatus comprising: a two dimensional array of modulatorand/or detector pixels disposed in a predetermined configuration, themodulator and/or detector pixels responding to applied electricalsignals to modulate and reflect light impinging the modulator and/ordetector pixels; an optical arrangement for directing a first incomingoptical beam from a first optical transmitter onto a first selected oneor ones of said modulator and/or detector pixels in said array and fordirecting a second incoming optical beam from a second opticaltransmitter onto a second selected one or ones of said modulator and/ordetector pixels in said array, the first incoming optical beam beingmodulated with data; and an electronic apparatus for storing the data onthe first incoming optical beam in memory and for modulating the secondincoming beam at said second selected one or ones of said modulatorand/or detector pixels in said array using said data stored in saidmemory; wherein the second incoming beam is reflected at said secondselected one or ones of said modulator and/or detector pixels via theoptical arrangement back to said second optical transmitter.
 19. Theoptical relay apparatus of claim 18 wherein the data on the firstincoming optical beam is stored in memory and thereafter the secondincoming beam is reflected at said second selected one or ones of saidmodulator and/or detector pixels via the optical arrangement back tosaid second optical transmitter modulated according to the data on thefirst incoming optical beam stored in memory.
 20. A method of addressingan array of AFP MQW pixels having first and second sets of electrodescomprising: (a) scanning the first set of electrodes to detect anysensing current resulting from the photoactivation of a pixel while thesecond set of electrodes is scanned with a small negative voltage; (b)if a pixel is detected in step (a) as being photoactivated, sampling anydata received by the photoactivated pixel in handshaking protocol todetermine whether a party photoactivating the photoactivated pixel isfriend or foe; (c) if the photoactivated pixel is turned on by a friend,applying a modulating voltage waveform to a corresponding electrode inthe second set of electrodes corresponding photoactivated pixel; and (d)if the photoactivated pixel is turned on by a foe, a voltage V, which isa zero reflection bias for the photoactivated pixel, is applied to acorresponding electrode in the second set of electrodes correspondingphotoactivated pixel.
 21. An optical apparatus comprising: atwo-dimensional array of modulator and/or detector pixels arranged in ahemispherical configuration, the modulator and/or detector pixelsresponding to applied electrical signals to modulate and reflect lightimpinging the modulator and/or detector pixels; and an opticalarrangement for directing an incoming optical beam from an opticaltransmitter onto a selected one or ones of said modulator and/ordetector pixels in said array and for returning light which is modulatedand reflected by said pixels to an optical transmitter from which theincoming beam was directed to the optical arrangement.
 22. The opticalapparatus of claim 21 further including electronic equipment for sensingwhen light impinges on said pixels and for supplying data signals tosaid pixels to cause said pixels to reflect the impinging light inaccordance with the data signals applied thereto.
 23. The opticalapparatus of claim 22 further including an associated electrical matrixfor connecting the modulator and/or detector pixels in said array to theelectronic equipment.
 24. The optical apparatus of claim 21 wherein thearray of modulator and/or detector pixels is an array of AsymmetricFabry-Perot Multiple Quantum Well devices.
 25. The optical apparatus ofclaim 24 wherein the optical arrangement is a lens which focuses theincoming beam onto said selected one or ones of said modulator and/ordetector pixels in said array.
 26. The optical apparatus of claim 21wherein the hemispherical configuration is defined by a flexible ordeformable body.
 27. The optical apparatus of claim 26 wherein theflexible or deformable body is a thermosetting plastic.
 28. The opticalapparatus of claim 27 wherein the flexible or deformable body is apolymer.
 29. The optical apparatus of claim 26 wherein the flexible ordeformable body has a sheet-like polymer support element in which thetwo dimensional array of modulator and/or detector pixels are embedded.30. The optical apparatus of claim 26 wherein the flexible or deformablebody is relatively plastic at temperatures above room temperature,thereby allowing the flexible or deformable body and the array ofmodulator and/or detector pixels embedded therein to conform to saidhemispherical configuration, while being relatively rigid at roomtemperature.
 31. The optical apparatus of claim 21 wherein eachmodulator pixel comprises a plurality of AFP MQW devices.
 32. Theoptical apparatus of claim 21 wherein each modulator pixel comprises atleast one AFP MQW device and at least one optically activated switchconnected in series with the at least one AFP MQW device.
 33. Theoptical apparatus of claim 21 wherein each modulator pixel comprises atleast one AFP MQW device and two optically activated switches connectedin series with the at least one AFP MQW device.
 34. The opticalapparatus of claim 21 wherein the modulator and/or detector pixels arearranged in an array separated by pixel addressing electrodes arrangedin a matrix, each modulator pixel having a pair of contacts forconnection to separate adjacent addressing electrodes.
 35. A method ofoptically repeating or relaying data comprising: disposing atwo-dimensional array of modulator and/or detector pixels in apredetermined configuration, the modulator and/or detector pixelsresponding to applied electrical signals to modulate and reflect lightimpinging the modulator and/or detector pixels; directing a firstincoming optical beam from a first optical transmitter onto a firstselected one or ones of said modulator and/or detector pixels in saidarray, the first incoming optical beam being modulated with data;directing a second incoming optical beam from a second opticaltransmitter onto a second selected one or ones of said modulator and/ordetector pixels in said arrays; detecting the data on the first incomingoptical beam; and modulating the second incoming beam at said secondselected one or ones of said modulator and/or detector pixels in saidarray using said data; wherein the second incoming beam is reflected atsaid second selected one or ones of said modulator and/or detectorpixels via the optical arrangement back to said second opticaltransmitter and is modulated by said data.
 36. The method of claim 35wherein the two dimensional array of modulator and/or detector pixels isdisposed in a hemispherical configuration.
 37. The method of claim 35further including temporarily storing data received from one source andmodulating a beam from another source with the temporarily stored data.38. A method of optically relaying data comprising: disposing a twodimensional array of modulator and/or detector pixels in a predeterminedconfiguration, the modulator and/or detector pixels responding toapplied electrical signals to modulate and reflect light impinging themodulator and/or detector pixels; directing a first incoming opticalbeam from a first optical transmitter onto a first selected one or onesof said modulator and/or detector pixels in said array, the firstincoming optical beam being modulated with data; directing a secondincoming optical beam from a second optical transmitter onto a secondselected one or ones of said modulator and/or detector pixels in saidarray; storing the data on the first incoming optical beam in memory;and modulating the second incoming beam at said second selected one orones of said modulator and/or detector pixels in said array using saiddata stored in said memory, wherein the second incoming beam isreflected at said second selected one or ones of said modulator and/ordetector pixels via the optical arrangement back to said second opticaltransmitter.
 39. A method of operating a Fabry-Perot multiple quantumwell structure both as an optical modulator and as an optical detectorby fixing a common electrical bias potential for both maximum detectionperformance when operating as a detector and optimum contrast ratio whenoperating as a modulator.
 40. An optical apparatus comprising: a twodimensional array of modulator and/or detector pixels embedded in aplurality of sub-wafers cooperatively arranged in a geometric shape, themodulator and/or detector pixels responding to applied electricalsignals to modulate and reflect light impinging the modulator and/ordetector pixels; and an optical arrangement for directing an incomingoptical beam from an optical transmitter onto a selected one or ones ofsaid modulator and/or detector pixels in said array and for returninglight which is modulated and reflected by said pixels to an opticaltransmitter from which the incoming beam was directed to the opticalarrangement.
 41. The optical apparatus of claim 40 further includingelectronic equipment for sensing when light impinges on said pixels andfor supplying data signals to said pixels to cause said pixels toreflect the impinging light in accordance with the data signals appliedthereto.
 42. The optical apparatus of claim 41 and an associatedelectrical matrix for connecting the modulator and/or detector pixels insaid array to the electronic equipment.
 43. The optical apparatus ofclaim 40 wherein the array of modulator and/or detector pixels is anarray of Asymmetric Fabry-Perot Multiple Quantum Well devices.
 44. Theoptical apparatus of claim 43 wherein the optical arrangement is a lenswhich focuses the incoming beam onto said selected one or ones of saidmodulator and/or detector pixels in said array.
 45. The opticalapparatus of claim 44 wherein the sub-wafers each have a generally flatpolygonal configuration.
 46. The optical apparatus of claim 45 whereinthe geometric shape is a hemispherical, geodesic configuration.
 47. Theoptical apparatus of claim 40 wherein the sub-wafers are a sheet-likeplastic support element having a thickness at least 20 times that of anindividual modulator pixel.
 48. The optical apparatus of claim 40wherein the sub-wafers are triangularly shaped.
 49. The opticalapparatus of claim 40 wherein each modulator pixel comprises a pluralityof AFP MQW devices.
 50. The optical apparatus of claim 40 wherein eachmodulator pixel comprises at least one AFP MQW device and at least oneoptically activated switch connected in series with the at least one AFPMQW device.
 51. The optical apparatus of claim 40 wherein each modulatorpixel comprises at least one AFP MQW device and two optically activatedswitches connected in series with the at least one AFP MQW device. 52.The optical apparatus of claim 40 wherein the modulator and/or detectorpixels are arranged in an array separated by pixel addressing electrodesarranged in a matrix, each modulator pixel having a pair of contacts forconnection to separate adjacent addressing electrodes.
 53. An opticalapparatus comprising: (a) a two dimensional array of individuallyaddressable modulator and/or detector pixels arranged in a geometricshape, (b) an optical arrangement for directing an incoming optical beamfrom an optical transmitter onto a selected one or ones of saidmodulator and/or detector pixels in said array; and (c) a controlapparatus for individually controlling the individually addressablemodulator and/or detector pixels to (i) reflect light which is modulatedand reflected by said pixels when the optical beam is from an authorizedor friendly source and (ii) inhibit optical reflection by theindividually addressable modulator and/or detector pixels when theoptical beam is not from an authorized or friendly source.
 54. Theapparatus of claim 53 wherein the individually addressable modulatorand/or detector pixels are each monolithic devices.
 55. The apparatus ofclaim 53 wherein the individually addressable modulator and/or detectorpixels are each asymmetric Fabry-Perot multiple quantum well devices.56. The apparatus of claim 55 wherein the individually addressableasymmetric Fabry-Perot multiple quantum well devices each have at leasttwo states of operation depending on how the individually addressableasymmetric Fabry-Perot multiple quantum well devices are controlled bythe control apparatus, the at least two states including: i. a detectionstate during which individually addressable asymmetric Fabry-Perotmultiple quantum well devices reflect little or no light, but do detectthe presence of incoming light, the control apparatus determiningwhether or not the incoming light detected by the individuallyaddressable asymmetric Fabry-Perot multiple quantum well devices is froman authorized or friendly source; and ii. a reflection state duringwhich individually addressable asymmetric Fabry-Perot multiple quantumwell devices modulate and reflect incoming light when the incoming lightto the individually addressable asymmetric Fabry-Perot multiple quantumwell devices is from one or more authorized or friendly sources asdetermined by the control apparatus.